Even should you not have a Sphero lying this model can create an interesting printable toy around.
2015 09 30 UPGRADE: Added STL variations in a zipped archive file for download.
IF I HAD THE TIME: I 'd develop a custom "top guide", for the 3 pronged component inside the sphero, for just two magnets to sit down in and keep the head facing forwards. or I 'd develop a weighted piece that replaces Sphero. Perhaps someone else needs to take on either challenge (someone without a full time occupation, children, as well as a honey-do-list).
Working from Lilykill's great version the foundation has been rescaled and slit in to halves for convenience and easy use with a Sphero.
NOTICE for perfectionist: I scaled up the foundation somewhat to 74mm that makes the outer diameter of the foundation somewhat bigger in relation to the first Sphero but it appears to create the robot go freely and matches the inner diameter of the first.
This first variant needs the Sphero to cut open and glue a magnet to interior 3
NOTE: I Have attempted a few distinct magnet mixes and have not discovered positioning or the perfect combination. (more detail after)
Additionally contained is a variant of the head for resin printers. It's hole with two drain holes at the bottom.
Some interesting testing with the kids:
Constructed using resources from the Ross School's Innovation Lab.
Still uncertain of the most effective method to print this and I imagine it is going to depend on your own printer... but I Have printed the head of this on a Ultimaker 2 in white PLA and had some really fine prints with merely a brim. I've really tried the half world with only a brim but the interior top place was too rough for the tight tolerances of the Sphero and he or she would get stuck.
I am not convinced the quality would be worth the difficulty in this instance although I've been able to print it on a Form1+ in white resin with some success.
So the Sphero can spin indoors the trick is printing it and having an extremely smooth interior.